Re: [PATCH 1/5] all: s390: move wrapper infrastructure to generic headers

[Heiko Carstens]

On Tue, Feb 02, 2016 at 11:41:56PM +0300, Yury Norov wrote:
> On Tue, Feb 02, 2016 at 08:54:34PM +0100, Heiko Carstens wrote:
> > So I think I can summarize my point to: if you can enforce correctness, why
> > shouldn't you do it if the performance impact is only a single instruction.
> 
> For aarch64 it's 5 instructions. But what's more important (if ever),
> another wrapper takes another i-cache line...
>         <compat_SyS_ftruncate>:
>         stp     x29, x30, [sp,#-16]!
>         mov     x29, sp
>         bl      d40 <do_sys_ftruncate.constprop.3>
>         ldp     x29, x30, [sp],#16
>         ret

Why does gcc allocate a stackframe here? Don't you have tail call
optimization?